1. Field of the Invention
The present invention relates to an automobile steering wheel and a manufacturing method therefore. More specifically, the present invention aims to improve the accuracy of the final product""s shape and to simplify the manufacturing steps therefore by employing for the steering wheel core member an arrangement in which a first resin layer is formed about a metal core bar.
This application is based on patent application No. Hei 11-252311 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Automobile steering wheels are available in a number of design variations, and may be manufactured by numerous methods. Basically, however, the method employed is one in which an outer shell, consisting of resin, wood, leather or the like, is formed around a metal core bar consisting of a metal material.
The metal core bar is formed using a metal pipe for example, and by welding together the rim, spokes and other parts into an assembly. Deformations in the metal core bar can readily occur during the welding process, however, with the rim being particularly prone to distortion.
When forming the outer shell by adhering a member to the metal core bar, deformities in the metal core bar can affect the outer shape of the steering wheel. As a result, accuracy in the shape of the final product is impaired.
For example, FIGS. 7A and 7B are diagrams disclosed in Japanese Patent Application, First Publication No. Hei 11-34881 and are an example of a conventional method for manufacturing a steering wheel. FIG. 7A is a planar view of a steering wheel, and FIG. 7B is a cross-sectional view taken along line Zxe2x80x94Z shown in FIG. 7A. In the figures, the numeral 12 indicates the metal core bar for the rim which is formed from a steel pipe or the like. In the method for manufacturing the steering wheel in this example, a wood member 16 consisting of a wooden material and/or a hard resin is adhered to metal core bar 12. A coating is performed to wood member 16, while at the same time an adhesive layer 20 is formed over the surface of metal core bar 12. The coating layer 22 on wood member 16 and the adhesive layer 20 on metal core bar 12 consist of the same material. Next, a leather support piece 24 consisting of a hard resin is fixed in place at a site adjacent to the end of wood member 16. A soft sheath 18 is formed onto adhesive layer 20 by injection molding a soft resin. Soft sheath 18 provides the base for the leather wrapping. Leather wrapping layer 26 is formed by wrapping a leather material around soft sheath 18 and leather support piece 24. Both edges of the leather are held in the space above a spacer 24a that is formed between leather support piece 24 and wood member 16.
When manufacturing a steering wheel using this type of method, if there is poor accuracy in the shape of metal core bar 12 so that distortion in metal core bar 12 occurs, it is difficult to attach the preformed hard wood member 16 to the correct position. In order to attach wood member 16 accurately, an approach must be employed in which the distortion in metal core bar 12 is absorbed by increasing the thickness of the adhesive layer for adhering metal core bar 12 and wood member 16. However, this approach is problematic as it leads to higher material costs due to the increased amount of adhesive agent that is used.
Moreover, since the manner of distortion will vary for each metal core bar 12, the application of the adhesive for metal core bar 12 and wood member 16 must be adjusted as required for each case. For this reason, it is not possible to employ a mechanized continuous process. As a result, the manufacturing operation for the steering wheel become complicated and requires more time.
In addition, when determining the positioning for adhering wood member 16 to metal core bar 12, the position is adjusted while observing the disposition of wood member 16 over the entirely of metal core bar 12. Thus, a large jig is required for supporting the entire body including metal core bar 12 and wood member 16. This is inconvenient as it also results in a poorer operability.
It is therefore the objective of the present invention to resolve at least one of the above-described problems encountered in the manufacture of a steering wheel. Specifically, the present invention aims to enable very efficient manufacture of a steering wheel with a highly accurate shape, even if deformation is present in the metal core bar. The present invention further aims to simplify the manufacturing steps for a steering wheel.
The present invention""s steering wheel manufacturing method is provided with a step for preparing a metal core bar, a step for forming a resin layer around the metal core bar to form a core member, a step for preparing a plurality of outer parts, which have a outer surface comprising a designed surface layer and an inner surface made of resin and a step for attaching said plurality of outer parts to the core member.
The core member for the steering wheel in the present invention is achieved by forming a first resin layer around a metal core bar.
In the present invention, a steering wheel is manufactured by forming a first resin layer about a metal core bar to produce a steering wheel core member, and then attaching outer parts to the outside of this steering wheel core member. As a result, the steering wheel core member produced has a highly accurate shape even if there is poor accuracy in the shape of the metal core bar. Accordingly, it is possible to manufacture a steering wheel of a specific shape with good accuracy and high efficiency. In addition, it is possible to reduce the amount of adhesive agent employed as compared to the conventional method in which distortion in the metal core bar is corrected via the adhesive layer. Thus, manufacturing costs are reduced and the adhering step is simplified.
Further, a first engaging member may be formed on a surface of the first resin layer, a second engaging member may by form on inner surface of the outer parts. By engaging the first engaging member with the second engaging member in the step for attaching the outer parts to the core member, positioning of the outer parts and the core member becomes an easy matter. Thus, operability is improved and the need for a large jig is eliminated. The manufacturing process therefore becomes simple. Moreover, depending on the design of the engaging member, it may be possible to reduce the number of parts.
The steering wheel manufactured according to the present invention""s manufacturing method has a highly accurate shape, good yield, and a reduced manufacturing cost.